This invention relates to the caps of writing instruments more particularly it relates to the cap of a writing instrument (hereinafter referred to as "a writing instrument's cap", when applicable) which has a vent structure for preventing suffocation of an infant if the cap of a writing instrument is swallowed by accident.
A writing instrument's cap having such vent has been disclosed in the art (cf. DT Patent No. 3821195, U.S. Pat. No. 4,969,766, and UK Patent Laid-Open No. 2215279). The cap is of a dual structure having a main cylinder and an inner cylinder. A gap is formed in the junction of the main cylinder and the inner cylinder to establish communication between the interior of the cap and the ambient atmosphere.
However, a writing instrument's cap having a vent structure in its inner cylinder has not been disclosed yet.
In the above-described conventional writing instrument's cap, it is difficult to form the main cylinder of metal or wood.